The present invention generally relates to a system and method for improving the navigation accuracy of an electromagnetic navigation system for use with medical applications. Particularly, the present invention relates to a system and method for verifying the accuracy of a surgical navigation system.
Electromagnetic type navigation systems are useful in numerous applications. One application of particular use is in medical applications, and more specifically, image guided surgery. Typical image guided surgical systems acquire a set of images of an operative region of a patient's body and track a surgical tool or instrument in relation to one or more sets of coordinates. At the present time, such systems have been developed or proposed for a number of surgical procedures such as brain surgery and arthroscopic procedures on the knee, wrist, shoulder or spine, as well as certain types of angiography, cardiac or other interventional radiological procedures and biopsies. Such procedures may also involve preoperative or intra-operative x-ray images being taken to correct the position or otherwise navigate a tool or instrument involved in the procedure in relation to anatomical features of interest. For example, such tracking may be useful for the placement of an elongated probe, radiation needle, fastener or other article in tissue or bone that is internal or is otherwise positioned so that it is difficult to view directly.
An electromagnetic tracking system may be used in conjunction with an x-ray system. For example, an electromagnetic tracking system may be used in conjunction with a C-arm fluoroscope. The C-arm fluoroscope may utilize an x-ray source at one end of the C-arm and an x-ray detector, or camera, at the other end of the C-arm. The patient may be placed between the x-ray source and the x-ray detector. X-rays may pass from the x-ray source, through the patient, to the x-ray detector where an image is captured. The electromagnetic tracking system may generate an electromagnetic field between the ends of the C-arm so tracking may continue during a surgical procedure.
Currently, an operating surgeon can assess the accuracy of the surgical navigation system in a subjective manner. A surgeon may visually compare the “predicted location” of the navigation instrument with the “actual location” of the same instrument on the intra-operative navigated images acquired during surgery. In current fluoroscopic navigation systems, this process may be referred to as “confirmation shots.”
For example, a surgeon may track the “predicted location” of the surgical instrument being used on the navigated fluoroscope image. The surgeon may set up the surgical instrument trajectory defining the surgical planning for the procedure being performed. By leaving the surgical instrument in the planned trajectory in the field of view of the C-arm, the navigation system may display the predicted location of the surgical instrument on the navigated fluoroscope image. The surgeon may then acquire an X-ray image, also called a confirmation shot, and captures it to the navigation screen. The predicted location of the surgical instrument and its actual location, materialized by its radiographic shadow on the navigated image, are visible on the navigated image. The predicted location of the surgical instrument is then superimposed on the navigated image.
By comparing the predicted location of the surgical instrument superimposed on the navigated image with the actual location, which may be shown as a shadow of the surgical instrument, the surgeon may assess the overall system accuracy. If the predicted location matches the actual location on the navigated image, the surgeon may determine the navigation system is accurate. If there is a visible difference between the predicted and actual instrument locations, the surgeon can conclude that the system error is high such that it makes the surgical navigation inaccurate and as a consequence, unsuitable for being used.
One disadvantage to the technique described above is that it provides a subjective method from which the surgeon makes a judgment on whether the navigation system is accurate enough to use. Using this technique to determine whether a navigation system is sufficiently accurate may vary from surgeon to surgeon. Also, a user relying on the navigation system knowing it has some degree of inaccuracy may not have confidence in the navigation system. This may compromise the effectiveness of the navigation system during the surgery.
Accordingly, a system and method is needed to better assess the accuracy of an instrument navigation system. Such a system and method may automate the verification procedure for assessing accuracy of the instrument navigation system.